Electric lamp



July 18, 1939. w. J. HlTcHcocK 2,166,781

ELECTRIC LAMP 3 Sheets-Sheet 1 July 18, 1939.

w. J. HITCHCOCK ELECTRICv LAMP Filed June 4, 19:56

3 SheeLs-Shee'fl 2 PR/MRY TERMINAL `fico/W71! RY TERNI/VAL July 1S, 1939. w, J. HITCHCOCK 2,166,781

ELECTRIC LAMP Filed vJune 4, 1936 3 Sheets-Shet 3 INVENTOR UCM JM Patented July 18, 1939 stares einem" ortica Application June 4,

4 Claims.

My invention relates to electric lamps of improved light output and better color, particularly `when secured by having moderate amounts of energy in the form of moving electrons, or light, incident upon substances-that emit visible' light, or luminesce, when so excited. It includes a structure which deals with the principles whereby the electric current ordinarily supplied for incandescent lamps may be used to generate the high frequency or high voltage usually advantageous in this sort of lamp and whereby a practical form of seal, economical of the space Within the lamp base, is particularly suited to the exhaust of lamps having doublewalled bulbs, or to the exhaust of lamps that it would be desirable to ll with a greater amount of gas than that corresponding to atmospheric pressure and normal' temperatures, such as some incandescent lamps. The arrangement for generating a high voltage consists of a Tesla coil if withinthe bulb. When without the bulb, it consists of an iron cored transformer of a particular form in which a high inductance may be secured in a small volume of space or of-an ordinary iron cored transformer.

It will be remembered that some cathode ray oscillograph tubes produce a spot of light by the impact of a beam of electrons upon the luminescent substance zinc silicate, or Willemite. As is well known, this impact is inherently an eilicient method of light production. If no energy is wasted forming a beam of the electrons or in the ohmic resistance inherent in returning the electrons to the cathode by a. path including leakage over glass or discharge through a low pressure gas, the eiliciency of light productionrfor total power consumed can much exceed that of a, tungsten filament incandescent; especially, as is well known, if the electrons hit with velocities corresponding to something more than those attained by falling through about a thousand volts. My anode is arranged in close proximity `to the luminescent material when light is excited by electron impact, which is' at high electron velocities. A further principle of operation arises from the well known similarity of electrons and photons in such processes as these and in a lamp designed to excite the luminescence of such materials as zinc silicate by the impact of photons rather than electrons the principle underlying my invention resides in a compact arrangement to develop a radio frequency4 and a high voltage within an outer enclosure occupied by an ionizable gas which then emits light, not necessarily wholly of a visible sort, but which if partly in- 1936, Serial No. 83,571`

visible is transformed into light of a wavelength visible to the eye by an appropriate choice of luminescent material. The anode of the electrical circuit need not be closely adjacent to the photofluminescent material, but some light may also be developed by the direct impact of electrons withinra highly evacuated interior space housing the generator of radio frequency electromagnetic waves.

uA further principle underlying my invention resides in the means whereby such interior spaces may conveniently be evacuated: a seal excluding the 'at phere from the interior of the lamp which uch facilitates arrangements of its parts and ontacts requiring little weight and space. Thes seals combine leading-in conductors, stem, and a bor in one structureLlargely dispense with the nec y for a flare, and consist of a metallic tube enclosing at least one electrical leading-in conductor electrically insulated from the metallic tube by a length of glass tubing and a glass bulb melted down upon the exterior wall of the metallic tube in a gas tight manner, the glass tubing also being melted down in a gas tight manner upon the interior wall of the metallic tube and the exterior wall of the leading-in conductor so that the lamp is sealed oil from the atmosphere. It will also be made clear that several different bulbs 'may be exhausted after they'have been assembled together; A particular method of making external contacts, useful even for radio tubes, will also be illustrated. No special materials different fromthose commonly used in forming leadingg-in conductors are needed for these specially shaped leading-in conductors and, as is Well known in the art, if the leading-in conductor consists of copper or copper sheathed drietal, it is necessary to borate its surface to have a. gas tight union with glass. It is geny erhlly advantageous to apply the heat for mak- 40 ing these seals gas tight by means of a radio frequency oscillator exciting eddy currents in a collar of well conducting metal, such as copper or nickel plated copper attached to the exterior of the metallic tube, which heats with the result that the glass insulator within the collar and the metallic tube is heated locally until it melts. When this is done, it is-advantageous to make the rest of the metallic tube of some less well conducting material, such as the cobaltnickel-iron alloys or chromium alloys now much used for radio tubes and sometimes sold under the trade name of 52 metal, as then the tube need be less thin to -stay cool.v Alloys of the ferrous group of metals or so called stainless steels must 55 be used if the lamps contain mercury, most other metals being. considerably attacked by it, even having an ordinary stem and base, a single bulb with material luminescent under electron impact on its inner wall, and containing an ordinary radio tube arranged to oscillate at a high frequency and generate a high voltage in a. secondary or Tesla coil adjacent to the bulb wall.

Figure 2 is a section takenl on the line 2-2 oi Figure l looking in the direction of the arrows.

Figure 3 is a vertical section through a lamp similar to that of Figure 1 except'the lamp has a.

stem and base facilitating its exhaust and assembly. 'I'he lamp has a double walled bulb and is provided with an ionizable gas or vapor in the space between the two bulbs, and a luminescent coating on the exterior of the outer bulb.

Figure 4 is a section taken on the line 4--4 of Figure 3 looking in the direction of the arrows.

Figure 5 is a vertical section of a lamp having a stem and base assembly containing a transformer in a base shaped portion, a single bulb with luminescent material on its walls, and anodes adjacent to the bulb walls. vAn indirectly heated cathode is provided in the center of the bulb. The stem is shaped to electrically contact Jack shaped conductors within the-base'shaped portion.

Figure 6 is a'section taken on the line 9--9 of Figure 5 ylooking in the'direction of the arrows.

Figure '7 is a fragmentary perspective view of substantially one coil of the transformer of the lamp of Figure 5.

Figure 8 is a fragmentary sectional view, partly diagrammatic, of the coil oi the transformer of Figure 5.

Figure 9 is a circuit diagram for the lamp of Figure 5l and its transformer.

Figure 10 shows a lamp similar in its essentials to the lamp of Figures 5 to -9 inclusive but having as simple a construction "as possible, an ordinary stem .and leading-in conductor assembly,

and an.anode surface on which designs or 1et,`v

` tering may conveniently be applied in materials luminescent under the impact of electrons in differing and contrasting colors. f

Figure 11 is a section taken on the line Il--M of the vertical section of Figure `101ooking in the I direction of the arrows.

Referring `to Figures 1 and 2, the lamp assembly consists oi the ordinary brass base Illettached to the bulb H with basing cement, and provided with the usual glass insulator l2,

through which the lead wire 25 passes and sol- -ders to the cap I3 at the point I4.

These arrangements are identical with those usual in'incandescent lamps and the stem has theusual 'being .that its cathodev also serves' as a source of thermionic electrons exciting the luminescent coating Ha. The cathode circuit consists of the terior of the bulb by the lead 36. 'I'he resistance 33 may if desired also be an incandescent tungsten lament, and may be a coiled lilament or a coiled coil lament, or it may be a resistance in any other form so long as it does not allow so much current to pass through the vacuum tube cathode that this is overheated when the current is switched on. A tungsten' incandescent iliament furnishes more instantaneous light at the instant ol turning on the lamp than an oxide coated filament but has the disadvantage of giving less thermionlc electron emission.

As to the grid circuit, a iiat'metal strip 30 is wound into the form of a solenoidal coil on a hot carbon mandrel having recesses to accommodate the glass rods 29. This is done at a temperature at which the glass will fuse to the metal and after cooling is rmly united with it. Any soft thin metal that is not volatile in vacuum may be used and nickel is preferred. The vacuum tube grid 23 connects to section 30h of coil 30 by the wire 31 part'of which is also' inserted in a glass bead 31h and helps in conjunction with collar'21 and supporting rods :28 to keep the asby means of the lead 38 to the conductor 25 which is the negative terminal of the circuit for i that portion of the time when alternating Ycurrent has the correct polarity to allow the lamp to function. If used 4on direct current this must be the negative terminal.

` The anode circuit proceeds from the base through the stem and press on the conductor 36, through a coil 34, thence by lead 3i to junction with the anode 2| of the vacuum tube. The circuit xis completed through the vacuum to the cathode by space currents as in theusualradlo vacuum tube but in addition the anode plate 2l is perforated and has a perforated cylindrical extension surrounding the further source of electrons I3 and through these perforations electrons capacity of the vacuum tube.

The general structure is such as is usual in radio tubes. A mica spacer 20 ls supported on hook wires I9 inserted in the glass button Ill which has been formed by the usual methods from the glass arbor I1. A. generally similar mica 'spacer is indicated at 22 and these two mica spacers serve to hold together the various parts of the vacuum tube. Another mica spacer 3| is employed in holding the glass rods 29 in position at their tops by any suitable means such as the hooks 32. Lavite or other electrically insulating material may be substituted for the micaA and glass without detriment. y

The operation of the devicewill be apparent from the following description taken in conjunction with the illustrationz--Electric power delivered to the vacuum tube causes it to generate radio frequency oscillations, at least on one half cycle of the supply frequency, depending somewhat on how much inductance is in series with leads and 36. These oscillations energize they Tesla coil which is so poled in section 30a as to generate a high positive anode voltage in the portion of it adjacentto coil 34 when the radio tube anode is at a positive potential. Both of these then oact to project considerable quantities of electrons from the thermionic surfaces 33 and 26 against the luminescentl coating lia. This then emits visible light, as in a cathode ray oscillograph tube, but over the entire luminescent surface and in considerable quantity due to the considerable current fiowing and the velocityr of the electrons at the time of theirA impact upon it due to the high positive voltagesecured by the transformer action ofthe Tesla coil co-operating with coil 3e. No considerable quantity of gas is present within the lamp which is initially highly evacuated and maintained in that state by the action of a silver-barium alloy getter from a cup 39 welded to a support wire 37d. This support wire does not contact the member 25 and is prevented from'short circuiting a portion of the Tesla coil 3B by the insulating glass bead 37b. As a result electrons are not slowed down by collision with gas during their passage from the cathodes to the luminescent coating which is also closely adjacent to the metal of the Tesla coil so there is also no great loss of power in ohmic resistance, even when ashing the getter has deposited no film perceptible to the eye. This results in a lamp having a greater output, measured in lumens per watt of power consumed, than the ordinary `tungsten incandescent when the vcolor of the light is the green-white of the luminescence of zinc silicate, and whenother materials are used, of other color when luminescent, of which there is a great variety well known to the art, it will generally be true that the lamp gives a greater number of lumens of light than an iri-` candescent of present ordinary commercial form and the same power consumption, at least when the incandescent is of the same color, approximately, as the luminescent lamp. There is; however, some interference with radio reception caused by the lamp of Figures 1 and 2 in that the radio frequency oscillations within the lamp start and stop on each cycle of the supply frequency when the lamp is used on alternating current and it appears that it is better to electrostatically and electromagnetically shield the lamp to prevent this, or supply the necessary high voltage at the same frequency as the supply frequency by means of a transformer with an' iron core, rather than get the lamps to oscillate continuously at a radio frequency by putting sufficient inductance in series with them so that their action as self re'ctifying units` would cause their terminals to be'supplied with direct current for all practical purposes. y

Figures 3 and 4 illustrate thestructure of Figures 1 and 2 electrostatically and electromagnetically shielded by enclosing it within an outer bulb IIb containing an ionizable gas such as mercury vapor, or mercury vapor and argon, at low pressure. As is well known, such gas becomes ionized and in an electric or electromagnetic field of high frequency and emits light without the necessity for any electrodes in the space containing it. As the ionized gas is also highly conductive of electricity, absorbing high frequency radiationi to produce light, itis also an effective shield against the passage of any radio frequency electromagnetic radiation from within it. Figures 3 and 4, besides illustrating this shield, also illustrate a structure for supplying the interior of the lamp with current which also serves to seal in, support, and exhaust the lamp; which processes are diflicult on account of having the Tesla coil of as great a diameter as possible and having it within an evacuated bulb surrounded by a bulb containing low pressure gas.

In Figures 3 and 4, certain reference characters '2t of the vacuum tube, similar to 33 in Figure 1 but in this modification it is preferred to make this a coiled coil tungsten filament, and by this means there is'some light the instant the lamp is switched on While there is no great disadvantage in lessening the thermionic emission from what it is in the former modification as in this present modification light produced by electron impact on a luminescent coating 46a on the inner wa-ll of the inner glass bulb d6, while produced in an analogous manner to that produced by the modification of Figures l and 2, in the modification' illustrated by Figures 3 and 4 is subordinate in importance to mercury discharge light, pro` duced by electrodeless discharge in the vapor from mercury droplet 41, and subordinate to a luminescence from a coating llc on the outer wall of an outer bulb i lb which luminescence is produced by an ultra-violet fraction of the light from the discharge in the mercury vapor. To produce this luminescence which might be described as a luminescence under the impact of photons, it is necessary that the glass of the outer bulb I Ib should be of some material such as quartz or the glass known as Corex which will be translucent to the ultraviolet mercury line of wavelength 2537. It is not necessary that the coating be on the wall of the bulb, it may be a paint upon the surface of a refiector or upon the wall of a room and may consist of a great variety of fluorescent substances of whichzinc silicate is one example, but which includes such substances as kerosene or coumarin, and may include substances melted into the outer wall of the bulb as Well as substances from'suspensions sprayedA on its exterior. Zinc oxide; for instance, may be mixed with lead borate and' a mixture of methanol and glycerine in about the proportions that would be used in making a bulb marking ink, for which silver oxide is 'used in place of zinc oxide, and this is applied to a bulb after ball milling the mixture which is then melted into the surface. There is some fluorescence from the zinc borate Vthat results from the heating.

For a like reason, where the light from luminescence under the direct impact of electrons is of subordinate importance, the secondary coil 5I, of Tesla coil, may be made as before or as illustrated in Figure 3, as an 'unsupported solenoid or bare wire partly out of contact with the wall of the bulb and the luminescent material thereon. If desired the luminescent material 46a may be omitted entirely and still produce a highlyef- :licient lamp. The primary coil 34a, of the Tesla 7 coil, is similar to coil 34 in the former modication but as illustrated in Figure 3 now couples inductively with a coil U in the grid circuit which is wholly separate from the secondary of the Tesla coil and can therefore be arranged somewhat more compactly. This coil is arranged in the grid circuit between the grid 23 and negative lead |4c. Together with the coil 34a, the secondary coil 5|, and the electrical capacities of the wiring and the vacuum tube, it forms a circuit oscillating at a radio frequency as in the modification of Figures l and 2. It will be clear that an additional condenser may be used if desired.

To assemble the lamp, metallic parts are spot welded together as in assembling a radio vacuum tube, suitable methods being well known in the art, and attached to a collar 4|a of heavy well conducting metal such as copper, which is nickel plated and firmly attached to a thin walled metallic tube 4l. Wire |4c, of fairly stout material, passes down the center of the metal tube 4| which is next surrounded by a closely fitting tube of glass 42 which has previously been flared somewhat where it is to `ioin the bulb 46, necessarily of a. somewhat wide mouthed sort but having no more clearance than isnecessary to allow of the inserting of coil 5| within it. The iiare and bulb are then heated until they are joined as ilustrated and the glass tube 42 is firmly unite to metallic tube 4|. lic tube 43 having a similar heavy collar of well conducting metal 45 is now. placed over the glass tube 42 and metallic tube 4| but not pushed all the way up on them. Nextbulb llb is placed in contact at its top with the top of bulb 46 so that its vopen end hangsaround the thin metal tube 43 to which it is now sealed, or united by fusion, at a place where metallic tube 43 includes no glass and in much the same fashion as if tube 43 were the leading-in wire of a neon sign lamp'electrode. In addition, if desired, care may also be taken l not to fuse the glass tube 42 to the metallic tube 43 by covering-tube 43 with a temporary' sleeve that is withdrawn just before the bulb unites with tube 43 oran air blast may be directed up within metallic tube 4| to keep the glass of tube 42 cool. The final appearance of the seal between the glass bulb IIb and metallic tube 43 is much that shown at llc and after the seal has been made it is pushed up over glass tube 42 until the outer bulb ||b is more or less concentric with the inner bulb 46 as illustrated soV that there will be a good thickness ot well conducting material all about the radio frequency oscillator when it is in operation. 'I'he next step in the assembly is to introduce a droplet of mercury 41 through the opening at 44 into the spacebetween the inner and outer bulbs. Then the bottom edge of tube 43 is crimped over the bottom of tube 42, as ls shown in the illustration', so as to hold the two bulbs in properY relative position, to each other and a length of `soft glass tubing 4|l is in serted within the metallic tube 4I with the wire |4c in the center of the glass. Air is now exhausted from within both bulbs by placing the metallic tube 43 in a-tightly tting rubber hose on an exhaust machine-or other pumping apparatus, just asis customary in making radio tubes or incandescent lamps.

When the exhaust of the inner bulb has been completed by methods wellknown to the art, the last step in the radio frequency heating is to heat the collar 4|a to a temperature suiiicient to render the glass tube somewhat molten and to Another thin metalv firmly melt it down upon and cause its attach ment to the metal of the tube 4| and the Wire |4c, thereby sealing off the inner bulb from the pump and later from the atmosphere. The outer bulb may now be exhausted without removing the lamp from the rubber and I have found. that this is best done not by the actionof heat and the pumpsalone but that it is also advisable to add a little argon gas to the mercury vapor within the outer bulb and cause a violet electrodeless discharge to iiow in the space between the inner and outer bulbs by means of an oscillator wholly -external to the lamp. This argon becomes quite impure and should be pumped off, whereupon the space between the bulbs may be reillled with pure argon and the lamp sealed oi by placing the high frequency oscillator coil in the neighborhood of the collar 45 ,as was done in the case of the inner bulb. This collar should be as close as possible to the Wall of the bulb ||b and of thicker metal` then the collar 4| as itwill be found that the ionized argon in the space between the bulbs has a marked shielding effect and much interferes with efforts to heat the collar 45 alone. Such eifects are less marked `with mercury vapor alone and can be minimized to any desired degree by controlling the pressure of mercury vapor through controlling the temperature of the liquid mercury. Collar 45 also should be kept as far as possible from the inner bulb so as to absorb little energy during the operation of the lamp and if desired may be omitted entirely and the lamp sealed off, at least as far as the space between the bulbs is concerned by a gas flame applied totube 43 externally to the outer bulb as is done in making a glass tip. It will also be evident that this particular method of sealing off the lamp is not an indlspensible method but merely aconvenient one; that this lamp may be evacuated if it has the same 'structure now common for lamps having an inner and outer bulb, so called double walled bulbs, if only electrical insulation is placed over the leading-in conductors into the inner bulbso that they cause no arc in the mercury vapor in the space between the bulbs as a consequenceA of their being at different electrical potentials.

After sealing the lamp off, it may be taken from the pump and a brass base Illa is'soldered to tube 43 at the point lb. Thereis no necessity for basing cement. This soldering is done with a gase ame having suiliciently concentrated heat to put `a small ball on the end of |4c, as shown at |4a, as a contact with the source of electric supply and to fuse. it firmly into the glass. The other contact is by way of the brass base, as is customary, and if tubes 4| and 431were not crimped together sufficiently before the exhaust to make good electrical contact now, they are Vsoldered to unite them firmly together so that tube 4| serves as a leading-in conductor by the connections shown to the coil 34a, the resistance 33, and through them to the other portions of the circuit and back to the other leading-in conductor |4c. If the lamp hasbeen sealed olf from the atmosphere with a gas name.V a cadmium-lead-tin solder is preferred at the point lub, otherwise a lead-tin or hard solder may be used without concern.

The operation of the lamp will now be generally described. So much of the lamp cf Flgures 3 and! as is within the inner bulb 46 will operate in a similar manner tothe lamp of Figvapor between the two bulbs 4B and I Ib. In addition, both visible light and ultraviolet light will come Afrom the electrodeless discharge in this space 4excited by the high frequency and high voltage within the inner bulb. This ultraviolet light may either be used as such, may be absorbed in the bulb` wall, ormay fall upon'a luminescent coating to produce visible light and if desired the lamp may be operated without the light coming from a coating luminescent under electron impact solely as a mercury lamp, or as a mercury lamp in conjunction with fluorescent materials. It will also be clear toA all skilled in the art, that many substances might be substituted for the mercury without departing from the spirit of the invention, such as sodium if the glass is such as to resist attack by sodium, or even sulphur if the metal of the seals is coated with material resistant to its chemical attack. In place of argon any of the inert gases may be used and if it is proposed to use an inert gas without the admixture of a vapor such as that of mercury, argon is not a particularly suitable gas to use as it gives little light by itself. Helium gives a yellowish white light and the striking red of neon is a matter of common knowledge.

Figures 5 to 9 inclusive illustrate a modification of the invention having a thermionic source -f electrons and two anodes alternately positive according to the phase of the alternating current supply. As before the exhaust is preferably such that electrons in their passage to a luminescent coating on the inner wall of the bulb are not impeded by collision with gas. This modification also has a stem generally similar to that illustrated in Figures 2 to 7 inclusive and through which it is exhausted in a similar 'manner but which serves in addition to make contact with terminals of a transformer in the form of split sleeves, generally similar to a telephone jack, arf ranged together with the transformer in a base shaped casing capable of being screwed into an ordinary lamp socket and into which the lamp proper is screwed. The transformer differs from that of the other modifications of the invention in being arranged forV full -wave rectification, in having an iron core, in being Without the lamp bulb, and in furnishing current and voltage at the frequency of the supply.

Describing the novel features of this modification more particularly from the drawings thereof as they appear in Figures 5 to 9 inclusive:--

a tungsten filament 24e is coiled on a thoria insulator 25e. This thoria insulator has an enlarged portion 25j which serves to hold the coil 24e in the center of a nickel cylinder 26e which has a cap of nickel mesh wire 26j and an. external coating of barium cxide'or other material 28g that readily emits thermionic electrons when heated; The nickel cylinder 26e is surrounded by a grid having two portions 23e and 23j electrically insulated from each other except through/the windings of a transformer but which connect by means of high resistances of fine coiled Wire wound on mica as at 49 and 48 respectively to v an outer screen also comprised of two portions ultraviolet light, and is provided with a step down transformer instead of a step up transformer which is preferred as is the case in the former modificatlons.- It seems advisable to show a droplet of mercury, as at 41a, similar to that of Figure 3, but it is preferred to have the lamp exhausted to a high vacuum.

The various portions of this modification of the invention which have been described are tied together and supported by two mica spacers 20e and 22e, in turn supported by suitable posts, and by a collar 21e fastened as illustrated to the glass tube -Mm. The seal consists as before preferably of alternate layers of glass and metal in the form of tubing surrounding a central wire or hollow metallic tube Mg. 'I'he wire tlg carries one leg of the current to heat the cathode and the other leg is carried by the collar 4ld and the specially shaped metallic flare llif which makes electrical contact with a base shaped portion ille. The wire lig is surrounded by an insulating glass tube Mh, which in turn is surrounded by a metallic tube t iz' carrying current for a' wire screen anode 30e. Conductor Mi in turn is surrounded by an insulator 4M of glass tubing and next by. another metallic tube dik carrying current for the anode 3f on the other half cycle. Conductor 41k in turn is surrounded by an insulator of glass tubing dim which before exhaust has had the metal part if carrying the heavy collar of Well con'- ducting metal Md sealed to it. Metal part luf is also sealed to the glass bulb. The seal is most conveniently made in much the same manner as before by assembling the interior metal parts and all the successive layers of glass and metal tubing except the innermost glass tube Mh which is inserted after the bulb has been attached to the metal part Illf and metal part If has been attached to at least the outermost layer of glass 4 lm by simultaneous fusion as in the other modiiications of the invention. Contact within the bulb, when not directly by a wire, is made by the collars 2lb, 4 lm, and attached wires. Within and without the bulb, the alternate layers of glass and metal are stepped on the end as shown to furnish electrically contacting surfaces.' Without the bulb, these 'register with and electrically contact two split sleeves |01' and Inh which are the secondary terminals of a high voltage transformer having a primary winding 52 and secondary windings 53 and 54 in electrical contact with each other and, by means of the wire 55, in electrical contact with the primary winding. This conductor Ih registers with and contacts conductor 4Ilc; conductor Ii registers with and contacts conductor 4h. lso a ball on the endof wire 4lg registers with a contact Ig insulated from the sleeve |011 by a short length of Bakelite tubing forced into the interior of sleeve |01. The sleeves lh and Ilii, the base shaped part |0e, and the core lllk upon which the transformer coils are wound consist of material of high magnetic permeability such as iron and its alloys. The primary power supply to the transformer is made by `contacts disposed, shaped, and insulated as in the case of an incandescent lamp base.

Ihe transformer, shown in purely diagrammatic fashion in the sketch of Figure 5 may be a transformer of the ordinary form with windings and connections appropriate to the operation of a vi'ull wave rectifier except the primary windings will generally furnish something more than about one thousand volts between the coating of luminescent material on the inner wall ofthe bulb and the thermionic cathode 26. That is to say, it may consist of an iron core of more or less toroidal form having electrically conducting windings separated into sections having, in general, different numbers of turns but all enclosing as far as possible the whole of the magnetic induction. I prefer; however, that the transformer of Figure be built as shown in detail in Figures 'I and ll Where the wires 50 of the winding are composites having a core of iron wire 66a covered with a layer of insulation 60h carrying a copper or silver wire 60o wound in' solenoldal fashion on the iron wire and its insulation as 4a. core or mandrel and exteriorly insulated as at 60d. This has, if desired, further secondary coils c and 60e' wound upon it in the same manner and insulated interiorly as shown at EM' and exteriorly as shown at B01'.

4Secondary and primary coils about the core tde have a mutual inductance since both enclose magnetic induction in the core tta. The arrangement will therefore act as a transformer ir respective of the form of the composite wire as a whole but as the composite wire acts similarly to i lan ordinary wire when coiled upon an iron torus it is preferably coiled in a more or less solenoidal form, as is illustrated in Figure '7, and placed upon an ordinary transformer core as illustrated by the transformer core Ik of Figure 8. The detail of Figure 8 illustrates a fragment in section of such a transformer winding composed of the composite wires. Appropriate taps are taken from the windings about .core a, before winding it on core Illk, so that these may serve in a full wave rectier circuit. If desired skips may be left in the windings to facilitate this, similar to the skips in tungsten lament coils, left to facilitate cutting theni to proper length.

Figure 9 is illustrative of the fact the operation of this modification of the invention is that of a full wave rectifier. This circuit beingstandard practice it requires no further description. The operation of this modification of the invention is generally similar lto that of the 'preceding modiflcations except that light is produced when electrons emerging from the cathode of the full wave rectifier strike upon that section of the inner wall of the bulb which is coated with material luminescent under electron impact and is adjacent to the half of the mesh which is anode, or electrically positive, on that particular half cycle. These electrons are. assisted in their passage to the rather remote anodes by voltages on the grids Il! and 23e like those on the anodes but never besldered. t

modifications of the invention depending upon.

the impact of electrons on luminescent substances. It is; however, somewhat more convenient to build a transformer for full wave rectification than for half wave rectiflcationvand twice the peak current, as is demanded in a lamp of equal light output to that operating on full wave rectification, when an'iron cored transformer is con- In case of half waverectiflcation for variations consisting merely of a glass bulb l0, nickel support Wires 1i conducting heating and space current to a fiat strip of barium oxide coated nickel-silicon alloy 14. The strip is thereby an'emitter of thermionic electrons and is cathode to an anode 12, of any metal commonly used in vacuum, and bearing a coating of materials luminescent under the impact of electrons in different colors as is illustrated at 1S. Zinc silicate; for instance, furnishes a green-white and calcium tungstate a blue. Other compounds, chiefly of the metals of the second column of the periodic table with amphoteric substances, may be used. Lettering or designs of one sort and. another is applied to the surface of the anode and becomes visible in contrasting colors under the impact of electrons. The shape of the anode is such as to adapt it to particular uses of this sort but if desired such designs may be applied to a glass bulb wall, although with less convenience. The cup l5 initially contains a get ter used to maintain a high vacuum.

Light is produced by the impact of electrons on the luminescent materials with great eiciency at 'high anode voltages similar to those of the modicatlons of Figures 1 to 4 inclusive and that of Figure 5. Light is also produced if no transformer of any sort is used and if instead a resistance is inserted in series between the line and the cathode, the other cathode terminal is connected directly to the line voltage, and the anode is connected to that side of the line which does not connect directly to the cathode, so that the voltage/'drop in the resistance is between the ano and the cathode of the lamp. As this is a very simple procedure, it is thought that lamps ope ated in this fashion mayhave some advertlsin value. The procedure is efficient at high line voltages and if desired a high line voltage may be'used and a transformer used merely to heat the cathode. It will be understood that the materials luminescent in different colors are applied toldiiferent portions of the anode and that some portions of the anode may have no coating of any sort and will therefore appear limitingithe scope of the invention to the e111--l vployment of its principles in these particular types of lamps, since the functions of the invention are applicable quite generally to many spel ciflc forms of devices in which the operation depends on supplying energy to materials to produce light as conveniently and economically as 1 possible.

the lamp of Figure 5 the necessary alterations in connections are so slight they will readily be understood. n k

Much variationl and simplification in the form of the lamp of Figure 5 ishowever possible. Figures 10 and 1l illustrate a particular one oi' these I claim: f l

i. An electric lamp-comprising a double walled bulb having an outer envelope at least partially permeable to light, luminous ionizable gas or apoibetween its inner and outer walls, and a urce of radio frequency electric oscillations within the inner wall of the said bulb.

2. An electric lamp comprising adouble walled bulb having an outer envelope at least partially permeable to light, luminous ionizable gas or vapor between its inner and outer walls, a source of radio frequency electric oscillations within the inner wall of the said bulb, and at least one wallV arcani within the inner wall ofthe said bulb. and a leading-in conductor oi' electric power from -an eirternal source of supply to the said radiation source wholly sheathed in an electrical insulator in the space between the inner and outer bulb walls.

4. An electric lamp comprising an evacuated envelope having a. wall at least partially permeabie to light, a source ofiree electrons sealed in said envelope, and a radio frequency electric oscillator in said envelope having a coil coupled therewith `and disposed between saidsource of free electrons and said wall, said coil developing a high voltage relative to said source of free electrons and being at approximately the same voltage as adjacent portions of said wall during its positive phase, said wall being provided with luminescent material exposed over an extensive area and in a substantially constant locality to 

